In order to improve safety of pedestrians, joggers, workers on roadways, etc., retroreflective markings have been attached to clothing. In one common embodiment, retroreflective appliques comprising a monolayer of retroreflective elements (e.g., transparent microspheres with hemispheric reflectors) partially embedded in a layer of binder material, with adhesive backings are bonded to articles of clothing. In other embodiments, the appliques are sewn onto a substrate.
A problem with such appliques is that their retroreflective performance tends to diminish unacceptably when the garment to which they are applied is washed. After just a few washings, the retroreflective brightness of the applique may be reduced to a small fraction, e.g., 5 percent or less, of its original brightness. This decrease is due to loss of retroreflective elements from the surface of the applique and/or degradation of the retroreflective elements, e.g., corrosion of aluminum hemispheric reflectors, during washing. As a result the visibility of the applique is reduced, thereby impairing the safety of the wearer.
The problem is particularly troublesome when the clothing is subjected to industrial laundering, where the conditions of laundering are often more severe than conventional home laundering. For instance, in an industrial laundry, the laundering conditions may include wash temperatures of 40.degree. to 90.degree. C. (105.degree. to 190.degree. F.) and pH of 10 to 12.5, whereas in contrast, typical conditions for home laundering may include temperatures of 4.degree. to 60.degree. C. (40.degree. to 140.degree. F.) and pH of less than 11. Also, home laundering equipment typically subjects the articles being cleaned to less rigorous handling and stress than does industrial laundry equipment.
In some embodiments, organosilane and/or zircoaluminate coupling agents have been used to improve the adhesion of the binder material to the retroreflective elements. Illustrative examples of previously known coupling agents include vinyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane, gamma-mercaptopropyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane, gamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, N-beta-(aminoethyl)gamma-aminopropyltrimethoxysilane, triaminofunctional trimethoxysilane, amino functional zircoaluminate, carboxy functional zircoaluminate, and mercapto functional zircoaluminate; used singly or in combination. Selection of coupling agent(s) is dependent in part upon the binder material and retroreflective elements used. To minimize fading of aluminum reflector layers, it is typically preferred that amino-containing silane coupling agents be avoided. Mercaptofunctional silane coupling agents typically exhibit a very objectionable odor. None of these coupling agents performs as well as desired in retroreflective appliques subjected to industrial wash conditions.